The "Face on Mars"

This is a really unusual mountain on Mars which looks like a face from atop,
and was discovered by the Viking orbiters in late 1976. Perhaps it resembles
somehow Australia's famous "Ayers Rock". The Mars Face rock gave rise to jokes,
science fiction, and space romanticism. The current (1996-8)
Mars Global Surveyor spacecraft has started to
investigate this landform further.

The sci.space FAQ (part 10)
gives account to and some data on the "Face on Mars":

There really is a big rock on Mars that looks remarkably like a humanoid
face. It appears in two different frames of Viking Orbiter imagery:
35A72 (much more facelike in appearance, and the one more often
published, with the Sun 10 degrees above western horizon) and 70A13
(with the Sun 27 degrees from the west). The feature, about 2.5 km
across, is located near 9 degrees longitude, +41 degrees N latitude,
near the border between region Arabia Terra and region Acidalia
Planitia.

Science writer Richard Hoagland has championed the idea that the Face is
artificial, intended to resemble a human, and erected by an
extraterrestrial civilization. Most other analysts concede that the
resemblance is most likely accidental. Other Viking images show a
smiley-faced crater and a lava flow resembling Kermit the Frog elsewhere
on Mars. There exists a Mars Anomalies Research Society (see address for
"Mars Research" below) to study the Face.

More detailed discussions of the Face, including raw and processed
imagery and discussion of plans for observation by the upcoming Mars
Global Surveyor, are at

R.C. Hoagland. The Monuments of Mars: A City on the Edge of Forever.
North Atlantic Books, Berkeley, California, USA, 1987. [Elaborate
discussion of evidence and speculation that formations near the Face
form a city]

B. O'Leary. Analysis of Images of the `Face' on Mars and Possible
Intelligent Origin. JBIS, Vol. 43 no. 5 (May 1990), p. 203-208.
[Lights Carlotto's model from the two angles and shows it's consistent;
shows that the Face doesn't look facelike if observed from the surface]

Mars Global Surveyor has now taken a
first hi-res image
of the Face and revealed that it is probably an interesting mountain or
mesa; no signs for an artefact are obvious (a fact which was not much
surprising for most investigators and scientists).
More on these results is in preparation.